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Anthropogenic mercury (Hg(0)) emissions oxidize to gaseous Hg(II) compounds, before deposition to Earth surface ecosystems. Atmospheric reduction of Hg(II) competes with deposition, thereby modifying the magnitude and pattern of Hg deposition. Global Hg models have postulated that Hg(II) reduction in the atmosphere occurs through aqueous-phase photoreduction that may take place in clouds. Here we report that experimental rainfall Hg(II) photoreduction rates are much slower than modelled rates. We compute absorption cross sections of Hg(II) compounds and show that fast gas-phase Hg(II) photolysis can dominate atmospheric mercury reduction and lead to a substantial increase in the modelled, global atmospheric Hg lifetime by a factor two. Models with Hg(II) photolysis show enhanced Hg(0) deposition to land, which may prolong recovery of aquatic ecosystems long after Hg emissions are lowered, due to the longer residence time of Hg in soils compared with the ocean. Fast Hg(II) photolysis substantially changes atmospheric Hg dynamics and requires further assessment at regional and local scales. Reduction of gaseous Hg(II) compounds drives atmospheric mercury wet and dry deposition to Earth surface ecosystems. Global Hg models assume this reduction takes place in clouds. Here the authors report a new gas-phase Hg photochemical mechanism that changes atmospheric mercury lifetime and its deposition to the surface.

Mercury (Hg), a global contaminant, is emitted mainly in its elemental form Hg⁰ to the atmosphere where it is oxidized to reactive HgII compounds, which efficiently deposit to surface ecosystems. Therefore, the chemical cycling between the elemental and oxidized Hg forms in the atmosphere determines the scale and geographical pattern of global Hg deposition. Recent advances in the photochemistry of gas-phase oxidized HgI and HgII species postulate their photodissociation back to Hg⁰ as a crucial step in the atmospheric Hg redox cycle. However, the significance of these photodissociation mechanisms on atmospheric Hg chemistry, lifetime, and surface deposition remains uncertain. Here we implement a comprehensive and quantitative mechanism of the photochemical and thermal atmospheric reactions between Hg⁰, HgI, and HgII species in a global model and evaluate the results against atmospheric Hg observations. We find that the photochemistry of HgI and HgII leads to insufficient Hg oxidation globally. The combined efficient photoreduction of HgI and HgII to Hg⁰ competes with thermal oxidation of Hg⁰, resulting in a large model overestimation of 99% of measured Hg⁰ and underestimation of 51% of oxidized Hg and ∼66% of HgII wet deposition. This in turn leads to a significant increase in the calculated global atmospheric Hg lifetime of 20 mo, which is unrealistically longer than the 3–6-mo range based on observed atmospheric Hg variability. These results show that the HgI and HgII photoreduction processes largely offset the efficiency of bromine-initiated Hg⁰ oxidation and reveal missing Hg oxidation processes in the troposphere.

Mercury is a persistent pollutant with significant public health impacts in polar regions where fish consumption drives human exposure. Atmospheric oxidation pathways control where mercury deposits globally, but the lack of molecular-level observations of oxidized mercury products has hindered the validation of proposed chemical mechanisms. Here, we show the in-situ online detection of individual mercuric halides (HgCl 2 , BrHgCl, HgBr 2 , ClHgI, BrHgI, and HgI 2 ) in the polar boundary layer using atmospheric pressure chemical ionization mass spectrometry. Our observations identify HgBr 2 as the dominant oxidized mercury species at both poles, while HgCl 2 and other halides were also observed in Antarctica. The observed speciation diverges from current model predictions, which favor HgCl 2 and HOHgBr as dominant oxidized forms. Our results show that real-time molecular measurements can substantially advance global mercury monitoring and improve the chemical models used to assess environmental policies and predict deposition patterns. Researchers report real-time molecular detection of oxidized mercury species in the polar atmosphere, revealing discrepancies with current models and advancing understanding of neurotoxic mercury cycling in sensitive ecosystems.

The atmospheric lifetime of mercury (Hg) determines its global spread and the delivery of this toxic pollutant to remote ecosystems. Previous studies have generally assumed that the chemical lifetime of elemental mercury (Hg 0 ) has remained constant across historical time periods, mirroring present‐day (PD, 2010–2019) conditions. However, since preindustrial times (PI, 1850) anthropogenic emissions have altered the concentrations of key oxidants that affect the Hg 0 lifetime, including bromine radicals (Br), hydroxyl radicals (OH), and ozone (O 3 ). Here, we use chemistry‐climate modeling to analyze the changes in Hg redox chemistry between PI and PD and consequent impacts on Hg transport and deposition. While increasing concentrations of OH and O 3 lead to 16% faster Hg 0 oxidation in the PD Northern Hemisphere, the increased partitioning of Br to reservoir species slows Hg 0 oxidation by 20% in the Southern Hemisphere compared to PI. On the global scale, these competing mechanisms lead to an overall buffering of the tropospheric chemical lifetime of Hg 0 . The shift from PI to PD atmospheric composition drives 15% more Hg deposition to tropical and subtropical fisheries, which are the major global source of toxic methylmercury for human exposure. The PI atmosphere was more conducive to the spread of Hg to the remote Southern Hemisphere extratropics, impacting the interpretation of historical records of Hg deposition from natural archives and the supply of Hg to the Southern Ocean marine sediment sink. This study reveals the previously overlooked role of changing atmospheric composition in aggravating human Hg exposure risk via altered deposition patterns. The distance that the toxic pollutant mercury (Hg) can be transported through the atmosphere is determined by how fast it oxidizes from its elemental form (Hg 0 ) into more soluble species. Since it is unknown how this oxidation chemistry has evolved over time, scientific studies have assumed that the timescales of Hg chemistry are fixed between different time periods. We challenge this assumption using a chemistry‐climate model to study Hg chemistry in the preindustrial (1850) and present‐day (2010–2019) atmospheres. Our results suggest that in the Northern Hemisphere atmospheric Hg 0 is oxidized more quickly in the present day compared to the preindustrial due to increases in two of its oxidants (ozone and hydroxyl radicals), while in the Southern Hemisphere the oxidation of Hg slows due to decreases in a different oxidant, the bromine atom. These regional oxidation changes shift the pattern of where Hg deposits to the surface. Specifically, changes in atmospheric chemistry have increased Hg delivery to tropical and subtropical oceans where tuna fisheries are located, raising the risk of human Hg exposure through fish consumption. The study highlights atmospheric chemistry as an overlooked factor that should be considered when analyzing historical records and future projections of Hg cycling. Atmospheric Hg redox chemistry has evolved over time due to changes in atmospheric composition, especially due to ozone, OH, and Br trends Present‐day atmospheric Hg 0 oxidation is faster in the Northern Hemisphere and slower in the Southern Hemisphere compared to preindustrial The shifts in Hg 0 oxidation enhance deposition to tropical and subtropical oceans, which are critical regions for Hg exposure risks

After recalling the basic relations relevant to both steady-state and time-resolved fluorescence polarization, it is shown how the values of steady-state polarized intensities recorded experimentally usually need to be corrected for systematic effects and errors, caused by instrumentation and sample properties. A list of selected reference values of steady-state fluorescence anisotropy and polarization is given. Attention is also paid to analysis of time-resolved fluorescence anisotropy data obtained by pulse fluorometry or phase and modulation fluorometry techniques. Recommendations for checking the accuracy of measurements are provided together with a list of selected time-resolved fluorescence anisotropy data as reported in the literature.

There is a striking disparity between the heart-shaped structure of human serum albumin (HSA) observed in single crystals and the elongated ellipsoid model used for decades to interpret the protein solution hydrodynamics at neutral pH. These two contrasting views could be reconciled if the protein were flexible enough to change its conformation in solution from that found in the crystal. To investigate this possibility we recorded the rotational motions in real time of an erythrosin-bovine serum albumin complex (Er-BSA) over an extended time range, using phosphorescence depolarization techniques. These measurements are consistent with the absence of independent motions of large protein segments in solution, in the time range from nanoseconds to fractions of milliseconds, and give a single rotational correlation time ϕ(BSA, 1 cP, 20°C) = 40 ± 2 ns. In addition, we report a detailed analysis of the protein hydrodynamics based on two bead-modeling methods. In the first, BSA was modeled as a triangular prismatic shell with optimized dimensions of 84 × 84 × 84 × 31.5 Å, whereas in the second, the atomic-level structure of HSA obtained from crystallographic data was used to build a much more refined rough-shell model. In both cases, the predicted and experimental rotational diffusion rate and other hydrodynamic parameters were in good agreement. Therefore, the overall conformation in neutral solution of BSA, as of HSA, should be rigid, in the sense indicated above, and very similar to the heart-shaped structure observed in HSA crystals.

Therapeutic application of many drugs is often hampered by poor or denied access to intracellular targets. A case in point is miltefosine (MT), an orally active antiparasitic drug, which becomes ineffective when parasites develop dysfunctional uptake systems. We report here the synthesis of a fluorescent BODIPY-embedding MT analogue with appropriate thiol functionalization allowing linkage to the cell-penetrating Tat(48-60) peptide through disulfide or thioether linkages. The resulting constructs are efficiently internalized into the otherwise MT-invulnerable R40 Leishmania strain, resulting in fast parasite killing, and hence successful avoidance of the resistance. In the disulfide-linked conjugate, an additional fluoro tag on the Tat moiety allows to monitor its reductive cleavage within the cytoplasm. Terminally differentiated cells such as peritoneal macrophages, impervious to MT unless infected by Leishmania, can uptake the drug in its Tat-conjugated form. The results afford proof-of-principle for using CPP vectors to avert drug resistance in parasites, and/or for tackling leishmaniasis by modulating macrophage uptake.

Marine organisms harbor diverse microbial communities on their surface, yet studies exploring the epibiotic bacteria of marine hosts remain largely unexplored, particularly in subantarctic ecosystems. Here, we cultured and isolated bacteria from the surface of three marine hosts: the centolla (the southern king crab; Lithodes santolla ), a squat lobster ( Grimothea gregaria ), and a brown macroalgae ( Macrocystis pyrifera ), from a subantarctic ecosystem, the Magellan Strait. Bacteria were inoculated in Petri dishes with Thiosulfate-Citrate-Bile Salts-Sucrose (TCBS) agar medium, and a fragment of the grown colonies was used to extract their DNA and sequence the whole 16S rRNA gene. We detected 14 different bacterial taxa, 11 from crustaceans, most of which were found only in the squat lobster. Vibrio spp. was detected in all marine hosts, but V. tasmaniensis was only detected in crustaceans. Phylogenetic comparisons revealed that epibiotic Vibrio formed a clade related to environmental Vibrio species, such as V. tasmaniensis , V. echinoidereum , and V. atlanticus . Given the ongoing climate change the world is experiencing, we explore the future sea surface temperatures that these bacteria might experience in the Magellan Strait. Oceanographic predictions indicate that the maximum sea surface temperatures will be 1 °C warmer in the future decades, and they could reach values above 14 °C in the last decades of the century. Our results increase the distribution and ecology of Vibrio bacteria and give insights about the temperatures that these microbes will face in future decades, which could have relevant consequences for aquaculture activities.

The toxicity and environmental applications of graphene oxide (GO) are largely unknown. The procedures involved in GO synthesis can impact biological responses and toxicity. In this study, the experimental methods involved in the synthesis of lyophilized sonicated graphene oxide (LSGO) followed by 1 h (1 h-LSGO) and 5 h sonication (5 h-LSGO), and the physicochemical characterization of both GOs is compared. A battery of toxicity tests performed with both GOs, using adenocarcinoma and fibroblast cells as representatives of the animal eukaryotic cell model, the bacteria Escherichia coli and Staphylococcus aureus as representatives of the prokaryotic model, and the microalga Chlorella vulgaris as representative of microalgae eukaryotic model, in a wide range (0.1–100 mg L −1 ) was developed, to find out possible differences between both LSGOs cytotoxicity on different biological models. In addition, physicochemical analysis of C. vulgaris exposed to both LSGOs, by scanning electronic microscopy and spectrofluorimetric analysis were performed. There was no cytotoxic effect (viability < 70%) on human alveolar adenocarcinoma A549 cells, nor to murine fibroblast L929 cells exposed to 1 h-LSGO and 5 h-LSGO. Similarly, no antibacterial activity against E. coli and S. aureus (0.1–100 mg L −1 of LSGO) was observed. Conversely, C. vulgaris responded with greater sensitivity than bacteria and animal cells, more relevant in 5 h-LSGO than in 1 h-LSGO, mainly in the higher GO concentration tested (100 mg L −1 ). These remarkable results could be attributed to the greater concentration of covalent bonds in 5 h-LSGO (~ 48% sp 2 , ~ 10% sp 3 ) than in 1 h-LSGO (~ 8% sp 2 , ~ 39% sp 3 ), and their interaction with the unsaturated fatty acids of the phospholipids of the microalgae´s membranes lipid bilayer. These relevant results report that 1 h-LSGO is nontoxic and can be used in biotechnological applications. On the other hand, GO and C. vulgaris are used as biofertilizers, so it is proposed to explore the potential biostimulant of the 1 h-LSGO- C. vulgaris consortium, among other environmental applications consistent with the sustainable agriculture approach. Graphical Abstract